Sophorolipids, formerly known as sophorosides, are glycolipid biosurfactants produced by yeast strains such as Starmerella (Candida) bombicola, Candida apicola, Candia bogoriensis, Candida batistae and Wickerhamilella domercqiae. They are composed of a disaccharide moiety linked to one hydroxyl group of one w or (w−1)-hydroxy fatty acid that is saturated or monounsaturated. The sugar moiety, i.e. sophorose or 2-O-glucopyranosyl-D-glucopyranose, may further show mono- or diacetylation at the 6′ and 6″ positions. The nature of the hydroxy fatty acid is characteristic, with the hydroxyl group being located on the n or n−1 carbon atom. The composition of the hydroxylated fatty acid varies depending on the production conditions. Lactonization frequently occurs between the carboxyl group and the 4″ OH group of the sophorose, providing sophorolactones in addition to sophorolipids in acid form. Hence, sophorolipids are considered as being a mixture of the compounds presented by the formula I, representing sophorolipids in lactone form, and by formula II, representing sophorolipids in acid form, in which 1. R′ and R″ represent hydrogen or an acetyl group, or 2. R′ is an acetyl group and R″″ a hydrogen group, or 3. R′ is hydrogen and R″ is an acetyl group, or 4. both R′ and R″ are hydrogen or 5. both R′ and R″ are acetyl groups. The molecules of formula I are lactonic sophorolipids, also called sophorolactones. The molecules of formula II are open ring sophorolipids, also called sophorolipids in acid form. The carbon chain length n may range from 2 to 17 carbon atoms. Typically the carbon chain length is 16 to 18 carbons long; that is n=13-15.
Sophorolipids are typically produced by fermentation processes wherein a glycolipid producing micro-organism is fed with a sugar supply and a substrate under appropriate fermentation conditions for the production of the sought sophorolipids.

The lactone form of sophorolipids has been found to lower surface tension more than does the acid form of sophorolipids. As many applications benefit from a lowering of surface tension and sophorolipids are obtained from renewable resources, sophorolactones are much sought for.
A sophorolactone composition is commercially available from the company Soliance. However, this product comprises relatively high amounts of water and sophorolipids in acid form as well as residual substrate (methyloleate and fatty acids) and is of amber color. This makes the product unsuitable for use in applications that should be substantially free of water and require sophorolactones in concentrated form. Although organic solvents can be used to extract and recover the sophorolactone, this is a highly cumbersome process and thus not economically interesting. Moreover it is often undesirable to have traces of organic solvents in the recovered product.
Unfortunately the currently available production methods provide sophorolactones as part of complex mixtures also comprising sophorolipids in acid form. Although solvents can be used to separate the lactone and acid forms, it is undesirable to have traces of organic solvents and in the end product.
It is known that sophorolactones are sensitive to hydrolysis. Hydrolysis leads to increased formation of the acid form which foams more heavily than the lactone form. It is highly desirable to have sophorolactone compositions which are less prone to hydrolysis, such that their characteristics remain stable and predictable over time.
Therefore there is a demand in the industry for sophorolactone compositions, which are less complex, highly concentrated, easy to formulate, less sensitive to hydrolysis.
It is an object of the present invention to provide concentrated sophorolactone compositions and derivatives with improved surfactant properties, such as hydrolytic stability, foaming behavior, decreased impurity levels, increased ease of handling and formulation. It is also an object of the present invention to provide uses for the sophorolactone compositions and derivatives of the invention.